1. Field of the Invention
This invention relates to peptidyl analogs that possess agonist or antagonist ghrelin activity and their therapeutic use thereof.
2. Description of the Prior Art
Ghrelin, a recently discovered orexigenic hormone, is produced as a preprohormone that is proteolytically processed to yield a peptide of the following sequence: H-Gly-Ser-Ser-Phe-Leu-Ser-Pro-Glu-His-Gln-Arg-Val-Gln-Gln-Arg-Lys-Glu-Ser-Lys-Lys-Pro-Pro-Ala-Lys-Leu-Gln-Pro-Arg-NH2 (SEQ ID NO:180); Kojima, M. et al., Nature, (1999), 402(6762):656-60). Ghrelin is produced by epithelial cells lining the fundus of the stomach and functions to stimulate appetite; its levels increase prior to a meal and decrease thereafter.
The native structures of ghrelin from several mammalian and non-mammalian species are known (Kaiya, H. et al., J. Biol. Chem., (2001), 276(44):40441-8; and International Patent Application PCT/JP00/04907 [WO 01/07475]). A core region present in ghrelin is responsible for activity observed at the GHS receptor which comprises the four N-terminal amino acids wherein the serine in the third position is normally modified with n-octanoic acid. In addition to acylation by n-octanoic acid, native ghrelin may also be acylated with n-decanoic acid (Kaiya, H. et al., J. Biol. Chem., (2001), 276(44):40441-8).
Ghrelin levels in the plasma of obese individuals are lower than those in leaner individuals and levels of ghrelin increase during the time of the day from midnight to dawn in thinner individuals suggesting a flaw in the circulatory systems of obese individuals (Yildiz, B. O. et al., Proc. Natl. Acad. Sci. USA, (2004), 101(28):10434-9). It has been found that individuals suffering from the eating disorder anorexia nervosa and patients who have cancer-induced cachexia have higher plasma levels of ghrelin (Garcia, J. M. et al., J. Clin. Endocrin. Metab., (2005), 90(5):2920-6).
In both animals and in humans, ghrelin powerfully stimulates growth hormone (GH) secretion from the anterior pituitary gland, mainly at the hypothalamic level, through its interaction with the GH secretagogue (GHS) receptor (GHS-R) (Ukkola, O. et al., Ann. Med., (2002), 34(2):102-8; and Kojima, M. et al., Nature, (1999), 402(6762):656-60). The GH-releasing activity of ghrelin is mediated by activation of GHS receptors at the pituitary and mainly at the hypothalamic level (Kojima, M. et al., Nature, (1999), 402(6762):656-60).
Prior to the discovery that ghrelin is a native ligand for the GHS receptor, it was known that the pulsatile release of GH from the pituitary somatotrops is regulated by two hypothalamic neuropeptides: GH-releasing hormone (GHRH) and somatostatin. GHRH stimulates the release of GH whereas somatostatin inhibits the secretion of GH (Frohman, L. A. et al., Endocr. Rev., (1986), 7(3):223-53; and Strobl, J. S. et al., Pharmacology Review (1994) 46:1-34). Ghrelin likely enhances the activity of GHRH-secreting neurons while concomitantly acting as a functional somatostatin antagonist (Ghigo, E. et al., Eur. J. Endocri., (1997), 136(5):445-60).
Release of GH from the pituitary somatotrops can also be controlled by GH-releasing peptides (GHRP). The hexapeptide His-D-Trp-Ala-Trp-D-Phe-Lys-amide (GHRP-6) was found to release GH from the somatotrops in a dose-dependent manner in several species, including man (Bowers, C. Y. et al., Endocrinology, (1984), 114(5):1537-45). Subsequent chemical studies on GHRP-6 led to the identification of other potent, synthetic GH secretagogues such as GHRP-I, GHRP-2 and hexarelin (Cheng, K. et al., Endocrinology, (1989), 124(6):2791-8; Bowers, C. Y., Novel GH-Releasing Peptides, Molecular and Clinical Advances in Pituitary Disorders, Ed: Melmed, S., Endocrine Research and Education, Inc., Los Angeles, Calif., USA, (1993), 153-7; and Deghenghi, R. et al., Life Sci., (1994), 54(18):1321-8). The structures of these three compounds are:
GHRP-IAla-His-D-(2′)-Nal-Ala-Trp-D-Phe-Lys-NH2; GHRP-2D-Ala-D-(2′)-Nal-Ala-Trp-D-Nal-Lys-NH2;and HexarelinHis-D-2-MeTrp-Ala-Trp-D-Phe-Lys-NH2.
A GHS can stimulate secretion of GH by a different mechanism than that of GHRH (Bowers, C. Y. et al., Endocrinology, (1984), 114(5):1537-45; Cheng, K. et al., Endocrinology, (1989), 124(6):2791-8; Bowers, C. Y., Novel GH-Releasing Peptides, Molecular and Clinical Advances in Pituitary Disorders, Ed: Melmed, S., Endocrine Research and Education, Inc., Los Angeles, Calif., USA, (1993), 153-7; and Deghenghi, R. et al., Life Sci., (1994), 54(18):1321-8).
The low oral bioavailability (<1%) of a peptidyl GHS encouraged the search for non-peptide compounds mimicking the action of GHRP-6 in the pituitary. Several benzolactams and spiroindanes have been reported to stimulate GH release in various animal species, including humans (Smith, R. G. et al., Science, (1993), 260(5114):1640-3; Patchett, A. A. et al., Proc. Natl. Acad. Sci. USA, (1995), 92(15):7001-5; Chen, M.-H. et al., Bioorg. Mod. Chem. Letts., (1996), 6(18):2163-8). A specific example of a small spiroindane is MK-0677 (Patchett, A. A. et al., Proc. Natl. Acad. Sci. USA, (1995), 92(15):7001-5):

The actions of a GHS (both peptide and non-peptide) appear to be mediated by a specific receptor (Howard, A. D. et al., Science, (1996), 273(5277):974-7; and Pong, S. S. et al., Mol. Endocri., (1996), 10(1):57-61). This receptor is present in the pituitary and hypothalamus of various mammalian species (GHSR1a) and is distinct from the GH-releasing hormone receptor. The GHS receptor was also detected in the other areas of the central nervous system and in peripheral tissues, for instance, adrenal, thyroidal, cardiac, pulmonary, renal and muscular (Chen, M.-H. et al., Bioorg. Med. Chem. Letts., (1996), 6(18):2163-9; Howard, A. D. et al., Science, (1996), 273(5277):974-7; Pong, S. S. et al., Mol. Endocri., (1996), 10(1):57-61; Guan, X.-M. et al., Mol. Brain. Res., (1997), 48(1):23-9; and McKee, K. K. et al., Genomics, (1997), 46(3):426-34). A truncated version of GHSR1a has been reported (Howard, A. D. et al., Science, (1996), 273(5277):974-7).
The GHS receptor is a G-protein coupled-receptor. The effects of GHS receptor activation include depolarization and inhibition of potassium channels, an increase in intercellular concentrations of inositol triphosphate (IP3) and a transient increase in the concentrations of intracellular calcium (Pong, S. S. et al., Mol. Endocri., (1996), 10(1):57-61; Guan, X.-M. et al., Mol. Brain. Res., (1997), 48(1):23-9; and McKee, K. K. et al., Genomics, (1997), 46(3):426-34).
GHS molecules such as ghrelin and its analogs have a variety of different therapeutic (U.S. Pat. No. 6,566,337; Inui, A., FASEB J., (2004), 18(3):439-56; Muller, E. E. et al., Neurobiol. Aging, (2002), 23(5):907-19; Casanueva, F. F. et al., Trends Endocrinol. Metab., (1999), 10(1):30-8; and Ankerson, M. et al., Drug Discovery Today, (1999), 4:497-506) and diagnostic uses. Compounds exhibiting agonist effects at the GHS receptor are indicated for improving a GH-deficient state (U.S. Pat. Nos. 6,861,409 and 6,967,237; and Casanueva, F. F. et al., Trends Endocrinol. Metab, (1999), 10(1):30-8), increasing muscle mass (U.S. Pat. Nos. 6,861,409 and 6,967,237) and/or physical strength (Ankerson, M. et al., Drug Discovery Today, (1999), 4:497-506), improving bone density (U.S. Pat. Nos. 6,861,409, 6,967,237 and 6,251,902; and Sibilia, V. et al., Growth Horm. IGF Res., (1999), 9(4):219-27), treating osteoporosis (International Patent Application Nos. PCT/IB96/01353 [WO 97/24369] and PCT/IB98/00873 [WO 98/58947]; and Casanueva, F. F. et al., Trends Endocrinol. Metab., (1999), 10(1):30-8), overcoming sexual dysfunction (U.S. Pat. No. 6,967,237; and Casanueva, F. F. et al., Trends Endocrinol. Metab., (1999) 10(1):30-8), treating cardiovascular disease (International Patent Application Nos. PCT/IB96/01353 [WO 97/24369] and PCT/IB98/00873 [WO 98/58947]; U.S. Pat. No. 6,251,902; De Gennaro Colonna, V. et al., Eur. J. Pharmacol., (1997), 334(2-3):201-7; and Casanueva, F. F. et al., Trends Endocrinol. Metab., (1999), 10(1):30-8), relieving arthritis pain (Granado, M., Am. J. Endo. Metab., (2005), 288:486-92), preventing or alleviating the onset of Alzheimer's disease (U.S. Pat. Nos. 6,686,359 and 6,566,337) and/or treating systemic lupus erythematosus or inflammatory bowel disease, e.g. Crohn's disease or ulcerative colitis (U.S. Patent Publication No. 2002/0013320).
Agonistic analogs of ghrelin can facilitate a gain in body weight (U.S. Pat. No. 6,967,237; Tschop, M. et al., Nature, (2000), 407(6806):908-13; and Tschop, M. et al., Endocrinology, (2002), 143(2):558-68) which in turn can be used to maintain a desired body weight (U.S. Pat. Nos. 6,861,409 and 6,967,237) and/or to recover physical function (U.S. Pat. Nos. 6,967,237 and 6,251,902; and International Patent Application No. PCT/IB96/01353 [WO 97/24369]).
Ghrelin also increases appetite (U.S. Pat. No. 6,967,237; and Okada, K. et al., Endocrinology, (1996), 137(11):5155-8). As such, ghrelin is often used to treat patients suffering from certain diseases or disorders or undertaking medicinal regimens which are traditionally accompanied with an undesirable weight loss such as: anorexia (U.S. Pat. No. 6,967,237; and Tschop, M. et al., Endocrinology, (2002), 143(2):558-68), bulimia (U.S. Pat. No. 6,967,237), cachexia (U.S. Pat. Nos. 6,967,237 and 6,251,902), particularly cancer-induced cachexia (U.S. Pat. No. 6,967,237; International Patent Appln. No. PCT/DK2004/000529 [WO 05/014032]; and Tschop, M. et al., Endocrinology, (2002), 143:558-68), AIDS (U.S. Pat. Nos. 6,861,409 and 6,967,237; and Tschop, M. et al., Endocrinology, (2002), 143(2):558-68), wasting syndrome in the frail and/or elderly (U.S. Pat. Nos. 6,861,409 and 6,967,237; International Patent Application No. PCT/IB96/01353 [WO 97/24369]; and Ankerson, M. et al., Drug Discovery Today, (1999) 4:497-506) and chronic renal failure (Casanueva, F. F. et al., Trends Endocri. Metab., (1999), 10(1):30-8). Medicinal treatments traditionally accompanied by a weight loss include chemotherapy, radiation therapy, temporary or permanent immobilization and/or dialysis (U.S. Pat. Nos. 6,967,237 and 6,251,902).
Obesity is a major risk factor for diabetes and a large fraction of non-insulin-dependent diabetes mellitus (otherwise referred to as “NIDDM”) patients are obese. Both conditions are characterized by elevated circulating insulin levels and suppressed GH levels. GH treatment of GH-deficient adults (Jorgensen, J. O. et al., Lancet, (1989), 1(8649):1221-5), obese women (Richelsen, B. et al., Am. J. Physiol., (1994), 266(2 Pt 1):E211-6) and elderly men (Rudman, D. et al., Horm. Res., (1991), 36 (Suppl 1):73-81) has been shown to produce increases in lean body, hepatic and muscle mass while decreasing fat mass. Accordingly, administration of a ghrelin agonist is an attractive therapy for obesity except for the diabetogenic effects of GH (U.S. Pat. No. 6,251,902; Ankerson, M. et al., Drug Discovery Today, (1999) 4:497-506; and Casanueva, F. F. et al., Trends Endocri. Metab., (1999), 10(1):30-8). Complications of diabetes such as retinopathy and/or for treating cardiovascular disorders (U.S. Pat. No. 6,967,237; and U.S. Patent Application Publication No. 2003/0211967) may be indirectly treated by ghrelin as well.
Paradoxically, ghrelin antagonists can be used to facilitate weight loss in an obese individual wherein said obesity is not due to the onset of NIDDM (U.S. Pat. No. 6,967,237; and U.S. Patent Application Publication No. 2003/0211967) as well as several other identified indications. Compounds exhibiting antagonist effects at the GHS receptor to promote the suppression of GH secretion, e.g., antagonist analogs of ghrelin, are indicated to reverse excessive GH secretion (U.S. Patent Application Publication No. 2002/0187938), to facilitate weight loss in the non-obese (U.S. Pat. No. 6,967,237), to maintain an ideal weight and/or to decrease appetite (U.S. Pat. No. 6,967,237). Excessive weight is a contributing factor to many diseases or conditions such as hypertension, dyslipidemia and cardiovascular disease (U.S. Patent Application Publication No. 2003/0211967; and U.S. Pat. No. 6,967,237) as well as gall stones, osteoarthritis (U.S. Pat. No. 6,967,237), certain cancers (U.S. Patent Application Publication Nos. 2003/0211967 and 2004/0157227; and U.S. Pat. No. 6,967,237) and Prader-Willi syndrome (U.S. Pat. No. 6,950,707; International Patent Application No. PCT/US2004/008385 [WO 04/084943]; Haqq, A. M. et al., J. Clin. Endocri. Metab., (2003), 88(1):174-8; and Cummings, D. E. et al., Nat. Med., (2002), 8(7):643-4). Ghrelin antagonists which facilitate weight loss would therefore reduce the likelihood of such diseases or conditions and/or comprise at least part of a treatment for such diseases or conditions. Antagonists of GHS molecules have also been disclosed to exhibit binding to tumorigenic tissue to result in a decrease in the number of tumorigenic cells in the target tissues, e.g. tumors in the lung, mammary glands, thyroid or pancreas (International Patent Application No. PCT/EP99/08662 [WO 00/29011]).
Analogs of GH secretagogues have also been employed to promote gastrointestinal motility, particularly in patients suffering from decreased gastrointestinal motility resulting from post-operative ileus or from gastroparesis incidental to the onset of diabetes or a chronic diabetic state (U.S. Pat. No. 6,548,501).
In addition, ghrelin has been effective in treating inflammation in a mammalian subject (International Patent Application No. PCT/US2005/016565 [WO 2005/110463]). In particular, the inflammation can be associated with a viral, bacterial, parasitic or fungal infection. Viral infections treatable with ghrelin may include Herpes simplex virus type-1, Herpes simplex virus type-2, Cytomegalovirus, Epstein-Barr virus, Varicella-zoster virus, Human herpesvirus 6, Human herpesvirus 7, Human herpesvirus 8, Variola virus, Vesicular stomatitis virus, Hepatitis A virus, Hepatitis B virus, Hepatitis C virus, Hepatitis D virus, Hepatitis E virus, Rhinovirus, Coronavirus, Influenza virus A, Influenza virus B. Measles virus, Polyomavirus, Human Papilomavirus, Respiratory syncytial virus, Adenovirus, Coxsackie virus, Dengue virus, Mumps virus, Poliovirus, Rabies virus, Rous sarcoma virus, Yellow fever virus, Ebola virus, Marburg virus, Lassa fever virus, Eastern Equine Encephalitis virus, Japanese Encephalitis virus, St. Louis Encephalitis virus, Murray Valley fever virus, West Nile virus, Rift Valley fever virus, Rotavirus A, Rotavirus B, Rotavirus C, Sindbis virus, Simian Immunodeficiency virus, Human T-cell Leukemia virustype-1, Hantavirus, Rubella virus, Simian Immunodeficiency virus, Human Immunodeficiency virus type-1 and Human Immunodeficiency virus type-2. (International Patent Application No. PCT/US2005/016565 [WO 2005/110463]). Bacterial infections that cause inflammation that can be treated with ghrelin (International Patent Application No. PCT/US2005/016565 [WO 2005/110463]) include M. tuberculosis, M bovis, M. bovis strain BCG, BCG substrains, M. avium, M intracellulare, M africanum, M kansasii, M marinum, M ulcerans, M. avium subspecies paratuberculosis, Nocardia asteroides, other Nocardia species, Legionella pneumophila, other Legionella species, Salmonella typhi, other Salmonella species, Shigella species, Yersinia pestis, Pasteurella haemolytica, Pasteurella multocida, other Pasteurella species, Actinobacillus pleuropneumoniae, Listeria monocytogenes, Listeria ivanovii, Brucella abortus, other Brucella species, Cowdria ruminantium, Chlamydia pneumoniae, Chlamydia trachomatis, Chlamydia psittaci, Coxiella burnetti, other Rickettsia species, Ehrlichia species, Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pyogenes, Streptococcus agalactiae, Bacillus anthracis, Escherichia coli, Vibrio cholerae, Campylobacter species, Neiserria meningitidis, Neiserria gonorrhea, Pseudomonas aeruginosa, other Pseudomonas species, Haemophilus influenzae, Haemophilus ducreyi, other Hemophilus species, Clostridium tetani, other Clostridium species, Yersinia enterolitica and other Yersinia species (International Patent Application No. PCT/US2005/016565 [WO 2005/110463]).
Inflammation treatable with ghrelin (International Patent Application No. PCT/US2005/016565 [WO 2005/110463]) can also be caused by parasites including Toxoplasma gondii, Plasmodium, Trypanosoma brucei, Trypanosoma cruzi, Leishmania, Schistosoma and Entamoeba histolytica or fungi such as Candida albicans, Cryptococcus neoformans, Histoplama capsulatum, Aspergillus fumigatus, Coccidiodes immitis, Paracoccidiodes brasiliensis, Blastomyces dermitidis, Pneomocystis carnii, Penicillium marneffi and Alternaria alternate (International Patent Application No. PCT/US2005/016565 [WO 2005/110463]).
Inflammation caused by liver toxicity or transplant rejection is also treatable by ghrelin (International Patent Application No. PCT/US2005/016565 [WO 2005/110463]). The liver toxicity may be associated with cancer therapy. In some instances, the cancer therapy, such as chemotherapy, may bring about liver toxicity. Liver toxicity brought about by both chemotherapy and apoptosis may be treatable by administration of ghrelin, ghrelin agonists or ghrelin antagonists (International Patent Application No. PCT/US2005/016565 [WO 2005/110463]).
Inflammation associated with cancer is also treatable with ghrelin (International Patent Application No. PCT/US2005/016565 [WO 2005/110463]). Such cancers include lymphoma, leukemia, mycosis fungoide, carcinoma, adenocarcinoma, sarcoma, glioma, blastoma, neuroblastoma, plasmacytoma, histiocytoma, melanoma, adenoma, hypoxic tumor, myeloma, AIDS-related lymphoma or AIDS-related sarcoma, metastatic cancer, bladder cancer, brain cancer, nervous system cancer, glioblastoma, ovarian cancer (International Patent Application No. PCT/AU02/00582 [WO 02/090387]; and Gaytan, F. et al., J. Clin. Endocri. Metab., (2005), 90(3):1798-804), skin cancer, liver cancer, squamous cell carcinomas of the mouth, throat, larynx, and lung, colon cancer, cervical cancer (International Patent Application No. PCT/AU02/00582 [WO 02/090387]), breast cancer (International Patent Application No. PCT/AU02/00582 [WO 02/090387]; and Cassoni, P. et al., J. Clin. Endocri. Metab., (2001), 86(4):1738-45), epithelial cancer, renal cancer (Jungwirth, A. et al., Proc. Natl. Acad. Sci. USA, (1997), 94(11):5810-3), genitourinary cancer, pulmonary cancer (Ghé, C. et al., Endocrinology, (2002), 143(2):484-91), esophageal carcinoma (Nwokolo, C. U. et al., Gut, (2003), 52(5):637-40), head and neck carcinoma (Jozkow, P. et al., Head Neck, (2005), 27(3):243-7), hematopoietic cancer, testicular cancer (Gaytan, F. et al., J. Clin. Endocri Metab., (2004), 89(1):400-9), colo-rectal cancer (Dagnaes-Hansen, H. et al., Anticancer Res., (2004), 24(6):3735), prostatic cancer (Jeffery, P. L. et al., Endocrinology, (2002), 172:R7-11), and pancreatic cancer (Volante, M. et al., J. Clin. Endocri. Metab., (2002), 87(3):1300-8); and International Patent Application No. PCT/US2005/016565 [WO 2005/110463]).
Finally, ghrelin has been shown to treat inflammatory diseases (International Patent Application No. PCT/US2005/016565 [WO 2005/110463]) such as asthma, reactive arthritis, hepatitis (Wallace, J. D. et al., J. Clin. Endocri. Metab., (2002), 87(6):2751-9), spondyarthritis, Sjogren's syndrome, Alzheimer's disease (U.S. Pat. Nos. 6,686,359 and 6,566,337; and Obermayr, R. P. et al., Gerontology, (2003), 49(3):191-5), and atopic dermatitis or inflammatory diseases associated with an autoimmune disease such as systemic lupus erythematosus, rheumatoid arthritis (Otero, M. et al., Rheumatology (Oxford), (2004), 43(3):306-10), systemic vasculitis, insulin dependent diabetes mellitus (Nieves-Riviera, F. et al., Growth Regul., (1993), 3:235-44), multiple sclerosis and muscular dystrophy (U.S. Patent Publication No. 2003/0139348), experimental allergic encephalomyelitis (Ikushima, H. et al., J. Immunol., (2003), 171:2769-72), psoriasis (Edmondson, S. R. et al., Endocri. Rev., (2003), 24(6):737-64), Crohn's disease (Slonim, A. E. et al., N. Engl. J. Med., (2000), 342(22):1633-7), inflammatory bowel disease (Chen, K. et al., Surgery, (1997), 121(2):212-8), ulcerative colitis, Addison's disease (Arvat, E. et al., Neuroendocrinology, (1999), 70(3):200-6), alopecia aretea, celiac disease (Peracchi, M. et al., Am. J. Gastroenterol., (2003), 98(11):2474-8); and Capristo, E. et al., Scand. J. Gastroenterol., (2005), 40(4):430-6), thyroid disease (Riis, A. L. et al., J. Clin. Endocrin. Metab., (2003), 88(2):853-7), and scleroderma. Inflammation as a result of a burn may also benefit from treatment with ghrelin as may inflammation of the lung (International Patent Application No. PCT/US2005/016565 [WO 2005/110463]). Inflammation may also cause a subject to lose appetite, particularly when the inflammation is low grade and/or in an aging subject (International Patent Application No. PCT/US2005/016565 [WO 2005/110463]).
Ghrelin antagonists can also be used to achieve a beneficial effect in a patient (U.S. Patent Publication Nos. 2002/187938, 2003/0211967 and 2004/0157227; and U.S. Pat. No. 6,967,237). For example, a ghrelin antagonist can be used to facilitate weight loss or decrease in appetite, to maintain an ideal body weight, to treat obesity, to manage a diabetic state including complications thereof such as retinopathy, and/or to treat cardiovascular disorders. Excessive weight is a contributing factor of several diverse diseases or conditions including, but not limited to, hypertension, diabetes, dyslipidemia, cardiovascular disease, gall stone formation, osteoarthritis and Prader-Willi syndrome as well as certain forms of cancers. Bringing about a weight loss can be used, for example, to reduce the likelihood of such diseases and as part of a treatment for such diseases.
Given the wide variety of beneficial effects that GHSs have to offer, there is a need in the art for effective agonist or antagonist ghrelin analog molecules.